1. Field of the Invention
The present invention relates to an electrochromic device.
2. Discussion of the Related Art
Electrochromic materials are materials which are capable of changing a color in reaction to an application of an electrical current. Specifically, the application of an electric current thereto effects an electrochemical reaction within such a material, thereby changing the color thereof.
A typical electrochromic device includes a laminated structure. The laminated structure includes an electrolyte ion conducting layer, an electrochromic layer, and a counter electrode layer. The electrolyte ion conducting layer is sandwiched between the electrochromic layer and the counter electrode layer. The laminated structure is then sandwiched between a pair of electrically conductive electrodes which are generally made of indium-tin oxide.
As is known, WO3 may change from a transparent state to a colored state. Therefore, many traditional electrochromic devices employ WO3 in the electrochromic layers. For instance, an electrochromic device employing WO3 as the electrochromic layer material includes a multilayer structure interposed between two glass plates. The multilayer structure sequentially includes: a first indium-tin oxide layer, a WO3 layer (i.e., the electrochromic layer), a Ta2O5 layer, a nickel oxide layer, and a second indium-tin oxide layer. The first and second indium-tin oxide layers function as electrodes. The Ta2O5 layer serves as an ion-introducing passage. The nickel oxide layer is configured for supplying ions. In operation, under the action of an electric field, the ions supplied by the nickel oxide layer are introduced into the WO3 layer through the Ta2O5 layer, whereby the color of the WO3 layer is changed.
However, the range of the color change of the WO3 layer is limited. During the ion removal and/or introduction processes, some ions may be captured by other layers and thereby cannot be introduced into the WO3 layer. As a result, with the amount of the ions available for activation of the WO3 layer decreasing, the color-changing performance of the electrochromic device is degraded accordingly. In addition, such a device has an unduly complicated structure.